THE EMPIRICAL FORMULA DETERMINATION OF LOCAL AND CODA MAGNITUDE FOR SUNDA STRAIT AND WESTERN PART OF JAVA

• Main Author: Safari Yogaswara, Debi
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/45766
• Institution: Institut Teknologi Bandung

In this research, we have determined the empirical formula of local and coda magnitude for Sunda Strait and Western part of Java to renewing the local magnitude scale formula which has been used by BMKG. The formulation of local and coda scale is developed from 1088 maximum amplitudes data of 158 earthquakes and 119 coda times of 34 earthquakes recorded on 14 seismic stations located around the Sunda Strait and Western part of Java. This study is conducted by picking the arrival time of P-wave, S-wave, maximum amplitude of S-wave phase and coda time. The obtained result will be converted in the form of magnitude, so the coefficient of model parameters on the basic equations of magnitude can be determined by linier inversion. Based on the results of the study, the ML scale for the Sunda Strait and Western part of Java is given by ????????=????????????(????)+1,154???????????? (????)+0,0035?????2,3416 in which A is vertical component ground displacement amplitude in nanometers. The amplitudes are measured after the signal simulated to the Wood–Anderson seismogram and r is the hypocentral distance (in km). The value of parameter b (0,0035) obtained is quite small, indicating that the Sunda Strait and Western part of Java regions have quite low attenuation levels. Based on the station correction values obtained shows that the amplification in most seismic station locations around the Sunda Strait and Western part of Java is quite high. The low attenuation and high amplification may be related to the geological condition of the study area which is dominated by sediment and soft rocks, such as alluvial deposits, sediments and sedimentary rocks, and volcanic rocks. Based on the comparison of the local magnitude values generated in this study against the local magnitude of the BMKG processing results, it can be concluded that the formulation of this study is quite consistent and more appropriate because it is made based on data in the study location. The empirical magnitude of the coda is ????????=0,8290????????????(????????????????????)+0,0004 ????+2,9931 in which ???????????????????? is the total duration in seconds of the earthquake recording from the P to the end of S-wave and r is the hypocentral distance (in km). However, the formulation of the magnitude of this coda is less representative and cannot be applied because the difference in the value of the coda magnitude to the local magnitude in the same event is quite large.